Gateway NV53 - Video Card upgrade

Would like to upgrade the video card on this little laptop to something the kid can use for his games - what can I put in it that will be compatible and not crash... I'm a techy but haven't done much upgrading on laptop hardware other than a screen, memory, and battery swap.

Currently is on Win 7 with the ATI Mobility Radeon HD 4200 that won't run his Guild Wars 2.